<!DOCTYPE html>
<html>

<head>
  <meta charset="utf-8">
</head>

<head>
  <script>
    function init() {
      // 获取弹窗
      var modal = document.getElementById('myModal');

      // 打开弹窗的按钮对象
      var btn = document.getElementById("myBtn");

      // 获取 <span> 元素，用于关闭弹窗
      var span = document.querySelector('.close');

      // 点击按钮打开弹窗
      btn.onclick = function () {
        modal.style.display = "block";
      }

      // 点击 <span> (x), 关闭弹窗
      span.onclick = function () {
        modal.style.display = "none";
      }

      // 在用户点击其他地方时，关闭弹窗
      window.onclick = function (event) {
        if (event.target == modal) {
          modal.style.display = "none";
        }
      }
    }

  </script>
  <style>
    /* 弹窗 (background) */
    .modal {
      display: none;
      /* 默认隐藏 */
      position: fixed;
      /* 固定定位 */
      z-index: 1;
      /* 设置在顶层 */
      left: 0;
      top: 0;
      width: 100%;
      height: 100%;
      overflow: auto;
      background-color: rgb(0, 0, 0);
      background-color: rgba(0, 0, 0, 0.4);
    }

    /* 弹窗内容 */
    .modal-content {
      background-color: #fefefe;
      margin: 15% auto;
      padding: 20px;
      border: 1px solid #888;
      width: 80%;
    }

    /* 关闭按钮 */
    .close {
      color: #aaa;
      float: right;
      font-size: 28px;
      font-weight: bold;
    }

    .close:hover,
    .close:focus {
      color: black;
      text-decoration: none;
      cursor: pointer;
    }
  </style>
</head>

<body onload="init()">
  <!-- 打开弹窗按钮 -->
  <button id="myBtn">打开弹窗</button>

  <!-- 弹窗 -->
  <div id="myModal" class="modal">

    <!-- 弹窗内容 -->
    <div class="modal-content">
      <span class="close">&times;</span>
      <p>弹窗中的文本...</p>
    </div>

  </div>

</body>

</html>